1. Field of the Invention
The present invention relates to the field of microelectronics fabrication and, more particularly, to a seamless trench-fill process utilizing sub-atmospheric pressure chemical vapor deposition (SACVD) technique.
2. Description of the Prior Art
Trench isolation techniques such as shallow trench isolation (STI) processes are known in the art. Generally, to form an STI isolation region on a substrate, a recess is first etched into the substrate, and then filled with an insulating dielectric film, which is typically a CVD silicon oxide film. Subsequently, a chemical mechanical polishing (CMP) process is carried out to provide a planar surface.
As the critical dimension of the integrated circuit devices shrinks to very deep sub-micron scale or beyond, it becomes more and more critical to fabricate reliable and effective device isolation in the art. However, conventional CVD methods have no longer provided satisfactory step coverage when dealing with high aspect ratio trenches, which are typically encountered in the fabrication of advanced integrated circuits. To overcome this, ozone-assisted sub-atmospheric pressure chemical vapor deposition (SACVD) techniques have been developed. Silicon oxide films employing the ozone-assisted SACVD techniques has superior gap filling ability that is particularly desirable for high aspect ratio trenches of limited trench dimension. After the SACVD film deposition, a high-temperature nitrogen anneal is performed to densify the deposited SACVD film. Typically, the densifying process is conducted in a furnace at a temperature no less than 1000° C.
However, the prior art SACVD techniques have several drawbacks when they are employed in the device isolation field. First, after the high-temperature anneal treatment, the deposited SACVD film is apt to shrink. For example, a shrinkage of about 7% has been observed after annealed at 1050° C. for 30 minutes. Besides, the film quality of the SACVD silicon oxide and its resistance to wet etchant are not high enough.
Another problem encountered when employing SACVD to form trench isolation regions is specifically depicted in FIG. 1. Since the SACVD film deposition is conformal and uniform along the sidewalls 22 of the trench 20, a seam defect 50 is left near the central line of the trench 20 when the trench is filled up. The seam defect 50 is concerned because it cannot be removed by mere high-temperature nitrogen anneal as mentioned supra, and because it is subject to corrosion or attacks by the wet etchant used in the subsequent wet cleaning procedures.
In light of the above, there is a need in this industry to provide an improved trench-fill process utilizing SACVD technique, which can produce a high-quality, seamless trench fill profile.